The initial alterations induced in bone marrow by leukemogenic doses of radiation will be examined. A variety of tissue culture methods will be utilized to propagate and enrich those target cells that can induce leukemia in adoptive transfer experiments. These altered target cells will be examined for their expression of ecotropic and recombinant virus in indicator co-cultivation assays. The cells will also be examined for alterations in endogenous proviral genetic elements by Southern analysis of restriction digests of their DNA. Similarly, the general location of known oncogenes will be analyzed in restriction digests and their expression will be measured by a quantitative dot blot hybridization assay. Expression of other transformation associated proteins and growth factors will be determined by metabolic synthesis assays using immunoprecipitation/-polyacrylamide gel analysis. Bioassays for growth factors such as interleukin 2 and 3 will be utilized to determine possible alterations in target cell expression of these and other growth factors. Marrow stromal capacity to support normal growth, and altered production of growth factors by radiated marrow stroma will also be examined during partial and complete leukemia induction protocols. Such studies will lead to a determination of obligate vs. coincidental alterations in bone marrow, resulting in generation of murine leukemia by ionizing radiation.